1. Field of the Invention
The present invention relates to a method of locating a vehicle on a track, and especially a rail vehicle on a rail track, enabling great accuracy to be obtained as to the position of the vehicle from an approximate measurement of the speed of the vehicle and a single inertial magnitude measured on board the vehicle.
The invention also relates to a location system implementing the method and which can be used in particular to control controlled systems intended to improve the comfort of passengers.
2. Description of the Prior Art
The simplest technique routinely employed for locating a rail vehicle on a rail track is to measure the distance traveled on the track from a starting point by integrating the speed of the vehicle. However, the speed of the vehicle is usually measured by measuring the rotation speed of the axles. The diameter of the wheels decreases as they wear down and the wheels skid when there is a high drive torque and low adhesion. Thus integrating the speed can lead to high errors between the measured position and the actual position of the vehicle after a few tens of kilometers.
Another prior art technique for locating a vehicle consists of equipping the rail tracks with beacons for precisely locating the rail vehicle on the track on which it is traveling. However, this technique has the disadvantage of making it necessary to install beacons along all the rail tracks of a rail network and its cost is therefore prohibitive. The technique consisting of locating a vehicle by means of the GPS system has the disadvantage of not enabling the vehicle to be located in shadow areas such as tunnels.
French patent application FR-99 07 435 filed by the applicant remedies the above disadvantages by locating a rail vehicle on a rail track by correlating a track profile calculated from the output of a plurality of inertial sensors disposed on board the vehicle with a map of the rail track stored during a previous journey. However, this kind of location technique requires the presence of a plurality of inertial sensors, which has the disadvantage that the sensors increase the cost of the rail vehicle. What is more, this kind of location method does not necessarily guarantee continuous location because it is based on searching a database for a correlation between measured values and a stored track profile.
The object of the invention is to alleviate the above disadvantages by proposing a method that allows accurate location of a vehicle on a track, by continuous convergence, without requiring additional trackside equipment, and using only one inertial sensor, so that it is simple and economical to implement.
The invention therefore provides a method of locating a rail vehicle on a rail track which includes the following steps:
measuring the speed of the vehicle at different times using means providing an approximate value of the actual speed of the vehicle;
measuring an inertial magnitude at different times using a single inertial sensor disposed on board the vehicle, the inertial magnitude being chosen to depend only on the speed of the vehicle and a geometrical characteristic specific to the track, such as the cant or the radius of curvature;
calculating the abscissa of the vehicle on the track by means of a convergent algorithm based on a non-linear observer, from known values of the measured approximate speed of the vehicle at different times preceding the time at which the vehicle is to be located, the measurements of the inertial magnitude and a database in which the geometrical characteristics specific to the track and its spatial derivative are stored for different curvilinear abscissae, the database being obtained by a learning process conducted beforehand.
According to another feature of the invention:
the speed Vm of the vehicle is measured at constant time intervals DTo, the measurements of the speed Vm(ti) being effected at times ti, ixcex5[1,N] of an observation time window To preceding the measurement time tN at which the vehicle is to be located and being stored in a memory;
the measurements of the inertial magnitude y(ti) effected on board the vehicle for the different times ti are stored in a memory;
an estimated curvilinear abscissa {tilde over (S)}N of the vehicle at the time tN is calculated by successive iteration, each new measurement time tN generating a new calculation iteration for which the observation window To is shifted by an amount DTo so that the starting point i=0 of the new observation window To coincides with the abscissa of the measurement point i=1 of the observation window To of the preceding iteration, the estimated curvilinear abscissa {tilde over (S)}N being calculated using the equation:                     s        ~            N        =                            s          ^                0            +                        ∑                      i            =            1                                i            =            N                          ⁢                  xe2x80x83                ⁢                                            V              ~                        i                    *                      DT            o                                ,      xe2x80x83    ⁢            with      ⁢              xe2x80x83            ⁢                        V          ~                i              =                  (                  1          +                      e            ⁡                          (                                                s                  ^                                0                            )                                      )            *              Vm        ⁡                  (                      t            i                    )                    
in which {tilde over (V)}i is the corrected speed of the vehicle at each time ti of the observation window To, e(ŝo) is the relative speed error and so is the corrected curvilinear abscissa of the starting point of the observation window To, e(ŝo) and so being obtained in the preceding iteration by a convergent algorithm based on a non-linear observer from measurements of the speed Vm(ti), the single inertial magnitude y(ti) at each time ti and the geometrical characteristic RO({tilde over (S)}i) and its spatial derivative DRO({tilde over (S)}i) at the level of the curvilinear abscissa {tilde over (S)}i estimated using the equation             s      ~        i    =                    s        ^            0        +                  ∑                  n          =          1                i            ⁢              xe2x80x83            ⁢                                    V            ~                    n                *                              DT            o                    .                    
The method according to the invention can further include one or more of the following features, individually or in any technically feasible combination
the database contains triplets (Sj, ROj, DROj) obtained by measuring the inertial magnitude y(Sj) at different abscissae sj during a previous journey of a vehicle along the track under operating conditions guaranteeing a precise knowledge of the data of the triplets;
for any estimated abscissa {tilde over (S)}i of the track the values of the geometrical characteristic RO({tilde over (S)}i) and the spatial derivative DRO({tilde over (S)}i) are calculated by interpolation between two triplets (Sj, ROj, DROj) stored in the database;
the inertial sensor is a yaw rate gyro;
the inertial sensor is a roll rate gyro;
the vehicle is a rail vehicle travelling along a rail track;
the method of locating a vehicle on a track is used to control controlled systems of a rail vehicle which have to be controlled in phase with the geometry of the track, such as a tilt system or an active transverse suspension system, recorded passenger announcements or a speed profile imposed on the vehicle.
The invention also provides a system for locating a vehicle on a track employing the above method and which includes:
measuring means providing the approximate speed of the vehicle;
a single inertial sensor;
a database in which a geometrical characteristic specific to the track and its spatial derivative for different curvilinear abscissae of the track are stored; and
a computer receiving the information from the speed measuring means and from the sensor, the computer being connected to the database to calculate the abscissa of the vehicle on the track.
Other features and advantages will emerge from the following description of one embodiment of a location method according to the invention, which description is given by way of example only and with reference to the accompanying drawings.